Silver Nanowire Electrodes Research Articles

Terahertz Analysis of CH3NH3PbI3 Perovskites Associated with Graphene and Silver Nanowire Electrodes.

In order to investigate the thermal and chemical (in)stabilities of MAPbI3 incorporated with graphene and silver nanowire (AgNW) electrodes, we employed the terahertz (THz) time-domain spectroscopy, which has a unique ability to deliver the information of electrical properties and the intermolecular bonding and crystalline nature of materials. In in situ THz spectroscopy of MAPbI3, we observed a slight blue-shift in frequency of the 2 THz phonon mode as temperatures increase across the tetragonal-cubic structural phase transition. For MAPbI3 with the graphene top electrode, no noticeable frequency shift is observed until the temperature reaches the maximum operating temperature of solar cells (85 °C). Phonon frequency shift is sensitive to the strain-induced tilt of PbI6 octahedra and our results indicate that graphene forms a stable interface with MAPbI3 and is also effective in suppression of the undesirable phase transition. Meanwhile, for MAPbI3 coupled with the AgNW bottom electrode, the THz conductivity was found to be as low as that of the MAPbI3 single layer, attributed to the chemical reaction between Ag atoms and iodide ions. The THz conductivity is greatly increased when an ultrathin Al2O3 interlayer is introduced to cover the AgNW network via the atomic layer deposition (ALD) method. ALD of Al2O3 on the AgNW surfaces at low temperature guarantees a conformal coating, which strongly affects the ohmic contacts between the NWs. Our results demonstrate the advantage of THz spectroscopy for the comprehensive analysis of thermal and chemical stabilities of perovskites associated with the electrode materials.

All-solution-processed, high-performance self-powered UVA photodetectors with non-opaque silver nanowires electrode

Extensive efforts have been made to develop novel transparent self-driven photodetectors to capture harmful ultraviolet light and to reduce energy consumption. Here, an all-solution-processed, high-performance self-powered UVA photodetector with non-opaque silver nanowires (Ag-NWs) electrode of > 80 % overall transparency is presented, which paves a way for devising efficient transparent electronics. The UVA photodetector ITO/ZnO(200 nm)/Ag-NWs possesses very low dark current of ∼ 10−11 A due to the large surface to volume ratio with a high On/Off ratio of 103 and a short-circuit current of 0.05 μA. A responsivity of 6 mA/W with a specific detectivity of 2.14 × 1011 Jones and the rising/decaying time of 360 ms/1.92 s were obtained under 45 μW/cm2 365 nm illumination at zero bias (i.e. in self-powered mode). This work uniquely combines the features of high optical transparency and self-power ability into UVA photodetectors and it would enable a broad range of optoelectronic applications.

Silver Nanowires Digital Printing for Inverted Flexible Semi‐Transparent Solar Cells

Transparent flexible organic solar cells (OSCs) are attracting increasing attention as an essential constituent for constructing smart window technologies and integrated photovoltaics (PVs). However, silver nanowire (AgNW) electrodes with negligible sheet resistance, good transmittance, and low costs are especially appealing in the design of flexible OSCs that require similar power conversion efficiency (PCE) values and superior flexibility compared with devices based on indium tin oxide (ITO) electrodes. Herein, the new digital printing technology of digital materials deposition to print the poly(3,4‐ethylene dioxythiophene):poly(styrene sulfonate) (PEDOT:PSS) as a hole transport layer and AgNWs as top and bottom electrodes for transparent flexible OSCs with an active layer as poly(3‐hexylthiophene) (P3HT):phenyl‐C61‐butyric acid methyl ester (PCBM) are used. All other thin layers are deposited on the polyethylene terephthalate (PET) substrate by the conventional process. The PV performance of the devices under inverted structure PET/AgNWs/ZnO/P3HT:PCBM/PEDOT/AgNWs is short circuit current density (Jsc) = 9.8 mA cm−2, open circuit voltage (Voc) = 0.53 V, fill factor (FF) = 0.60, and PCE = 2.9% with visible light transparency = 45%.

Observing and Understanding the Corrosion of Silver Nanowire Electrode by Precursor Reagents and MAPbI3 Film in Different Environmental Conditions

AbstractSince metal electrode is an important component in the perovskite solar cells, which can be used as back contact, transparent electrode, and the transparent interlayer of tandem devices, the corrosion of metal electrode by perovskite film, should be understood. Here, the corrosion of conventional reagents of organic–inorganic perovskite material, i.e., CH3NH3X (MAX) and PbX2, X = I, Br, and Cl, against silver nanowire (AgNW) based transparent electrode are investigated under four different environments, i.e., nitrogen protection, light irradiation, oxygen exposure, and moisture exposure, separately. The corrosion process is inspected by monitoring the time‐dependent resistance variation of the electrode coated by the film of precursor reagent. In addition, the perovskite film of CH3NH3PbI3 (MAPbI3) is also coated on the silver nanowire electrode without or with the hole transporting layer of poly(3,4‐ethylenedioxythiophene)–poly(styrenesulfonate) (PEDOT:PSS) or nanostructured CuSCN for understanding the corrosion process under different environmental conditions. The experimental results presented in this paper would be helpful to the understanding of metal electrode stability in perovskite solar cells.

Research on flexible silver nanowire electrode for organic light-emitting devices

By spin-coating silver nanowires (AgNWs) and polymethyl methacrylate (PMMA), applying pressure imprint and plasma treatment, we obtained flat AgNW thin film with a sheet resistance of 20 Ω/sq and a transmittance of 78% at 550 nm with low surface roughness. No significant change in sheet resistance was observed after cyclic bending (bending radius is 5 mm) test and tape test. After 1 000 bending tests, the change rate of sheet resistance was only 8.3%. The organic light-emitting devices (OLEDs) were prepared by using such AgNW electrodes and a maximum brightness of 5 090 cd/m2 was obtained. Compared with the AgNWs electrode without any treatment, the present AgNW electrodes have lower sheet resistance and better hole injection. Our results show spin-coated with flat layers, embossed and plasma-treated AgNW electrodes are suitable for manufacturing flexible organic optoelectronic devices.

Optimal Design of PEDOT:PSS Polymer-Based Silver Nanowire Electrodes for Realization of Flexible Polymer Solar Cells

In this study, polyethylene 2,6-naphthalate (PEN) was selected as a substrate to fabricate a flexible conducting electrode through the solution process. The sandwiched silver nanowire (AgNW) electrode between the poly(3,4-ethylenedioxythiophene):polystyrene sulfonate (PEDOT:PSS) layers fabricated on the flexible PEN substrate was successfully prepared, which exhibited a moderately high electrical conductivity and surface smoothness suitable for polymer solar cells. Notably, the sheet resistance of the PEDOT:PSS/AgNW/PEDOT:PSS film was 22 Ω/□, and it exhibited the transmittance of 82% at the wavelength of 550 nm, although PEN was used as the substrate. This electrode film can be easily employed as an anode, and when it is applied as an electrode in a polymer solar cell, it reveals a comparable performance to that of indium tin oxide-based devices. This simple and effective fabrication of flexible conductive electrodes is envisaged to contribute immensely to future research on flexible electronics and optoelectronics.

Recent progress in post treatment of silver nanowire electrodes for optoelectronic device applications.

Owing to the economical and practical solution synthesis and coating strategies, silver nanowires (AgNWs) have been considered as one of the most suitable alternative materials to replace commercial indium tin oxide (ITO) transparent electrodes. The primitive AgNW electrode cannot meet the requirements for preparing high performance optoelectronic devices due to its high contact resistance, large surface roughness and poor stability. Thus, various post-treatments for AgNW film optimization are needed before its actual applications, such as welding treatment to decrease contact resistance and passivation to increase film stability. This review investigates recent progress on the preparation and optimization of AgNWs. Moreover, some unique fabrication strategies to produce highly oriented AgNW films with unique anisotropic properties have also been carried out with detailed analysis. The representative devices based on the AgNW electrode have been summarized and discussed at the end of this review.

Capillary Force-Induced Printing of Stretchable and Mechanically Stable Silver Nanowire Electrodes With Highly Ordered Alignment For Ultra-Flexible Organic Light-Emitting Devices

Transparent conductive electrodes (TCEs) have attracted considerable attentions as one of the essential components in optoelectronic devices. High conductivity, transmittance and flexibility are required for the practical applications of the TCEs in wearable and portable electronics. Here, a simple fabrication process of capillary force-induced printing has been developed to realize highly aligned silver nanowires (AgNWs) film with high flexibility, stretchability and conformability. Ultrathin and skin-attachable OLEDs have been realized based on the aligned AgNWs electrode. This work has proposed a low-cost and fast fabrication strategy to realize highly aligned AgNWs electrode for the flexible and stretchable optoelectronic devices.

Microscopic Deformation Modes and Impact of Network Anisotropy on the Mechanical and Electrical Performance of Five-fold Twinned Silver Nanowire Electrodes

Microscopic Deformation Modes and Impact of Network Anisotropy on the Mechanical and Electrical Performance of Five-fold Twinned Silver Nanowire Electrodes

Microscopic Deformation Modes and Impact of Network Anisotropy on the Mechanical and Electrical Performance of Five-fold Twinned Silver Nanowire Electrodes.

Silver nanowire (AgNW) networks show excellent optical, electrical, and mechanical properties, which make them ideal candidates for transparent electrodes in flexible and stretchable devices. Various coating strategies and testing setups have been developed to further improve their stretchability and to evaluate their performance. Still, a comprehensive microscopic understanding of the relationship between mechanical and electrical failure is missing. In this work, the fundamental deformation modes of five-fold twinned AgNWs in anisotropic networks are studied by large-scale SEM straining tests that are directly correlated with corresponding changes in the resistance. A pronounced effect of the network anisotropy on the electrical performance is observed, which manifests itself in a one order of magnitude lower increase in resistance for networks strained perpendicular to the preferred wire orientation. Using a scale-bridging microscopy approach spanning from NW networks to single NWs to atomic-scale defects, we were able to identify three fundamental deformation modes of NWs, which together can explain this behavior: (i) correlated tensile fracture of NWs, (ii) kink formation due to compression of NWs in transverse direction, and (iii) NW bending caused by the interaction of NWs in the strained network. A key observation is the extreme deformability of AgNWs in compression. Considering HRTEM and MD simulations, this behavior can be attributed to specific defect processes in the five-fold twinned NW structure leading to the formation of NW kinks with grain boundaries combined with V-shaped surface reconstructions, both counteracting NW fracture. The detailed insights from this microscopic study can further improve fabrication and design strategies for transparent NW network electrodes.

Vertical Alignment of Nematic Liquid Crystals Based on Spontaneous Alignment Layer Formation between Silver Nanowire Networks and Nonionic Amphiphiles

The vertical arrangement of nematic liquid crystals (LCs) in displays can be generally achieved by introducing a polyimide material onto indium tin oxide electrodes. However, this method requires multiple coating and deposition processes as well as high curing temperature, restricting the potential applicability to flexible displays. Thus, we herein propose the facile approach for homeotropic alignment of nematic LCs based on spontaneous alignment layer formation between silver nanowire networks and nonionic amphiphiles. The silver nanowires as transparent electrode materials were spin-coated on glass substrate and 4-(4-heptylphenyl)benzoic acids as nonionic amphiphiles were doped into the LC medium. The nonionic amphiphiles were spontaneously bonded to the polyvinylpyrrolidone capping layer of silver nanowire networks through polar interactions, creating the self-assembled alignment layer of nonionic amphiphiles on silver nanowire electrodes. In addition, the alkyl chains of the amphiphiles interacted with the LC molecules, leading to stable directional LC alignment along vertical direction. The electro-optical characteristics of the manufactured LC cell were comparable to those of conventional device including polyimide layer and indium tin oxide electrode. Overall, the combination of silver nanowire electrode and nonionic amphiphiles presents a new way to achieve the vertical alignment of nematic LCs without polyimide layer.

Transparent Fused Nanowire Electrodes by Condensation Coefficient Modulation

AbstractSilver nanowire networks can offer exceptionally high performance as transparent electrodes for stretchable sensors, flexible optoelectronics, and energy harvesting devices. However, this type of electrode suffers from the triple drawbacks of complexity of fabrication, instability of the nanowire junctions, and high surface roughness, which limit electrode performance and utility. Here, a new concept in the fabrication of silver nanowire electrodes is reported that simultaneously addresses all three of these drawbacks, based on an electrospun nanofiber network and supporting substrate having silver vapor condensation coefficients of one and near‐zero, respectively. Consequently, when the whole substrate is exposed to silver vapor by simple thermal evaporation, metal selectively deposits onto the nanofiber network. The advantage of this approach is the simplicity, since there is no mask, chemical or dry metal etching step, or mesh transfer step. Additionally, the contact resistance between nanowires is zero and the surface roughness is sufficiently low for integration into organic photovoltaic devices. This new concept opens the door to continuous roll‐to‐roll fabrication of high‐performance fused silver nanowire electrodes for myriad potential applications.

Palladium-Coated Single Silver Nanowire Electrodes: Size-Dependent Voltammetry, Enhanced Chemical Stability, and High Performance for Methanol Oxidation.

Silver nanowires (AgNWs) have been extensively studied as promising nanomaterials in optics, next-generation flexible electronics, and energy-related fields, but the stability and the properties at single-nanowire level still need to be investigated carefully. We have successfully prepared single palladium@silver nanowire electrodes (Pd@AgNWEs) by using a laser-assisted pulling method, followed by a galvanic replacement reaction (GRR). The results show that the chemical stability of AgNWs can be improved greatly by coating a small amount of Pd, and the Pd@AgNWEs exhibit superior electrocatalytic performance in methanol oxidation. This work can give us a new insight to investigate the performance of devices/catalysts at the single-particle/nanowire level that will benefit research in flexible electronics and energy-related fields.

Water-assisted formation of highly conductive silver nanowire electrode for all solution-processed semi-transparent perovskite and organic solar cells

Transparent conductive electrode (TCE) is an essential part of modern optoelectronic devices. Silver nanowire (AgNW) is regarded as the most promising TCEs, owing to its balanced conductivity and transparency, and solution processability. The use of insulating polyvinyl pyrrolidone (PVP) surfactant limits the conductivity of the final AgNW networks. Herein, by introducing a small amount of deionized water into the AgNWs dispersion in isopropanol (IPA), the conductivity of the spray-coated AgNW electrode was significantly improved. Sheet resistance (Rs) of 27.0 Ω □−1 with transparency of 92% (at 550 nm) was obtained for the AgNW films spray coated from the AgNW ink with 20% water, which is much lower than the IPA-only AgNW film (120.9 Ω □−1 with similar transparency). Morphology analysis confirmed that water is able to wash PVP away from the AgNW surface and promote the formation of AgNW bundles, which increase the conductivity. The optimized AgNW ink was then used for perovskite and polymer solar cells. High power conversion efficiencies of 14.04% for perovskite solar cell and 6.44% for organic solar cells with averaged light transmittance of 21.7% and 33.12% are achieved, respectively, which are among the highest values for all solution-processed semi-transparent perovskite and polymer solar cells.

Operation Range-Optimized Silver Nanowire Through Junction Treatment

In past decades, stretchable conductors have been investigated for a wide range of applications, and the operation strain range of such devices varies by application. To commercialize stretchable devices, it is necessary to optimize the deformation of stretchable electrodes based on a given device elongation range. Therefore, we investigated the deformation mechanics of a silver nanowire (AgNW) electrode on an elastomeric substrate depending on its junction treatment method. At low-strain ( 20%), the thermally annealed AgNW electrode rapidly increased in resistance, while the laser-welded AgNW electrode showed lower resistivity change. By in situ surface analysis and a repetitive tensile test, we observed that the thermally annealed AgNW electrode shows less cracking at low strain but the laser-welded AgNW electrode exhibits fracturing of individual nanowires at low strain. Furthermore, at high strain, laser-welded AgNWs could slide to reduce stress during elongation, resulting in a smaller change in resistance compared to that of thermally annealed AgNW electrode. These results indicate that optimization of adhesion is necessary to fabricate stretchable devices based on deformation range.

High-Resolution Filtration Patterning of Silver Nanowire Electrodes for Flexible and Transparent Optoelectronic Devices.

Silver nanowire (AgNW) electrodes attract significant attention in flexible and transparent optoelectronic devices; however, high-resolution patterning of AgNW electrodes remains a considerable challenge. In this study, we have introduced a simple technique for high-resolution solution patterning of AgNW networks, based on simple filtration of AgNW solution on a patterned polyimide shadow mask. This solution process allows the smallest pattern size of AgNW electrodes, down to a width of 3.5 μm. In addition, we have demonstrated the potential of these patterned AgNW electrodes for applications in flexible optoelectronic devices, such as photodetectors. Specifically, for flexible and semitransparent UV photodetectors, AgNW electrodes are embedded in sputtered ZnO films to enhance the photocurrent by light scattering and trapping, which resulted in a significantly enhanced photocurrent (up to 800%) compared to devices based on AgNW electrodes mounted on top of ZnO films. In addition, our photodetector could be operated well under extremely bent conditions (bending radius of approximately 770 μm) and provide excellent durability even after 500 bending cycles.

A transparent flexible volatile memory with ultrahigh ON/OFF ratio and ultralow switching voltage

Here, a high-performance transparent flexible dynamic random access memory (DRAM) device on a polyvinyl alcohol (PVA) substrate is presented with silver nanowires (Ag NWs) serving as top and bottom electrodes, and hybrid silver nanoparticles (Ag NPs)-polyvinyl pyrrolidone (PVP) films serve as resistive-switching (RS) medium. The obtained memory cells show typical volatile RS behaviors with an ultrahigh ON/OFF current ratio of 10 8 and an ultralow switching voltage of 0.7 V. In particular, the fabricated flexible devices demonstrate excellent mechanically robust feature and great electrical stability during 100 dynamic bending tests, maintaining ~85% of transparency in the visible wavelength. This work provides an effective route to construct flexible and transparent polymer memory devices with high-performance. A transparent flexible polymer memory consisting of polyvinylpyrrolidone-silver nanoparticle composite switch sandwiched between silver nanowire electrodes with polyvinyl alcohol substrate was fabricated via a full solution method. The obtained device exhibited a high-performance volatile memory behavior with ultralow switching voltage and ultrahigh ON/OFF ratio as well as outstanding transparency and flexibility. • A high performance transparent flexible DRAM-type polymer memory was achieved. • The memory device was prepared basing on a full-solution processing method. • High OFF/ON current ratio of ~10 8 and low switching voltage of ~0.7 V was achieved. • Silver nanowires (Ag NWs) is essential for excellent transparency and flexibility.

A Skin‐Inspired, Interactive, and Flexible Optoelectronic Device with Hydrated Melanin Nanoparticles in a Protein Hydrogel–Elastomer Hybrid

AbstractMelanin, a biologically occurring pigment featuring broadband optical absorption, ion‐binding affinity including antioxidative and radical‐scavenging properties, and hydration‐dependent electrical conductivity is an ideal natural semiconducting material for interfacing electronics with biological systems. Here, a skin‐mimicking optoelectronic device with a melanin nanoparticle (MNP) dispersion in a protein hydrogel–elastomer hybrid (a mimic of epidermis/dermis layers with melanin) and its application as a dopamine sensor and a UV index meter are reported. MNPs dispersed in water are placed in the elastomer reservoir with integrated silver nanowire electrodes and a transparent silk hydrogel window cover; they exhibit n‐type semiconducting behavior with increased conductivities compared with those of dehydrated MNPs. Enhanced generation of free radicals by light illumination results in an increase of the electrical conductivity. In addition, the artificial optoelectronic skin interacts with its environment through the silk hydrogel window. Applications of the device, including its use as a dopamine sensor and a UV index meter to detect dopamine and UV light passing through the window, are demonstrated. The sensitivity of the dopamine sensor is enhanced by the light illumination.

Self-augmented ion blocking of sandwiched 2D/1D/2D electrode for solution processed high efficiency semitransparent perovskite solar cell

Perovskite solar cells (PSCs) have been emerged as a promising candidate for solution processable semitransparent (ST) and flexible photovoltaics. However, solution processing compatible transparent electrodes (TEs) still exist as one of the major obstacles for high efficiency and stable ST-PSCs. In this work, we constructed a sandwiched top transparent electrode by using solution processable one- and two-dimensional materials. The assembled 2D graphene with controlled reduction and 1D silver nanowires (AgNWs) electrode present significant contribution to carrier's collection and stability of devices. A self-augmented iodine ion blocking is observed, which mitigated the corrosion of TE from water, oxygen, iodine and etc.. The stability of unencapsulated ST-PSC devices has been significantly enhanced with >80% original power conversion efficiency maintained after 320 h discontinuous tests in the ambient atmosphere, comparing to <10% for AgNWs-along devices. A high-performance single junction ST-PSC was obtained with the efficiency reached up to 14.69% with the transmittance over 20% for visible light and 59% for near infrared ray. Thus, with the development of the printing compatible top 2D/1D/2D TE, the performance of all-solution processed ST-PSCs could be further enhanced and possibly applied for low-cost building integrated photovoltaics, tandem and portable electronic devices.

Intrinsically Stretchable Organic-Tribotronic-Transistor for Tactile Sensing.

Stretchable electronics are of great significance for the development of the next-generation smart interactive systems. Here, we propose an intrinsically stretchable organic tribotronic transistor (SOTT) without a top gate electrode, which is composed of a stretchable substrate, silver nanowire electrodes, semiconductor blends, and a nonpolar elastomer dielectric. The drain-source current of the SOTT can be modulated by external contact electrification with the dielectric layer. Under 0-50% stretching both parallel and perpendicular to the channel directions, the SOTT retains great output performance. After being stretched to 50% for thousands of cycles, the SOTT can survive with excellent stability. Moreover, the SOTT can be conformably attached to the human hand, which can be used for tactile signal perception in human-machine interaction and for controlling smart home devices and robots. This work has realized a stretchable tribotronic transistor as the tactile sensor for smart interaction, which has extended the application of tribotronics in the human-machine interface, wearable electronics, and robotics.